读dubbo源码笔记(一)
首先看Extension扩展,相当于dubbo最底层核心
如开发者所述:“Dubbo的扩展点加载从JDK标准的SPI(ServiceProviderInterface)扩展点发现机制加强而来。",基本上与ServiceLoader类似(童鞋们,可以先看ServiceLoader源码再来看这个,比较理解),但功能增强
增强了Wrapper包装,cachedActivates自动激活,Adaptive自适应,objectFactoryExtension实例的属性获取对象方式,这4类。
下面看源码,整个Extension扩展,最主要类就只有一个:ExtensionLoader
先来看ExtensionLoader属性:
private static final Logger logger = LoggerFactory.getLogger(ExtensionLoader.class); //loggerFactory是dubbo自己封装 了log4j\jdkLog而来的。找不到log4j就去jdklog private static final String SERVICES_DIRECTORY = "META-INF/services/";//静态,请看下面的地址,这个地方也可以配,但是如果自己又使用了ServiceLoader,2者会有冲突。 private static final String DUBBO_DIRECTORY = "META-INF/dubbo/";//静态,主要Extension扩展 的地方 private static final Pattern NAME_SEPARATOR = Pattern.compile("\\s*[,]+\\s*");//静态,这个不解释 private static final ConcurrentMap<Class<?>, ExtensionLoader<?>> EXTENSION_LOADERS = new ConcurrentHashMap<Class<?>, ExtensionLoader<?>>();//静态,放置所有ExtensionLoader private static final ConcurrentMap<Class<?>, Object> EXTENSION_INSTANCES = new ConcurrentHashMap<Class<?>, Object>();//静态,放置所有Extension 实例对象 private final Class<?> type; //ExtensionLoader实例所对应的接口Class private final ConcurrentMap<Class<?>, String> cachedNames = new ConcurrentHashMap<Class<?>, String>();//用于所有接口实现的Class 查找name,对于多name的取第一个 private final Reference<Map<String, Class<?>>> cachedClasses = new Reference<Map<String,Class<?>>>();//用于所有接口实现的name查找Class,对于多name,会存在 多name 对应一个Class private final Map<String, Activate> cachedActivates = new ConcurrentHashMap<String, Activate>();//自动激活用 private final ConcurrentMap<String, Reference<Object>> cachedInstances = new ConcurrentHashMap<String, Reference<Object>>();//本接口的实例 private volatile Class<?> cachedAdaptiveClass = null; private final Reference<Object> cachedAdaptiveInstance = new Reference<Object>();//自适应实例 private volatile Throwable createAdaptiveInstanceError; private Set<Class<?>> cachedWrapperClasses;//包装类Class private String cachedDefaultName;//默认使用扩展实例,由SPI注解value指定 private Map<String, IllegalStateException> exceptions = new ConcurrentHashMap<String, IllegalStateException>(); private final ExtensionFactory objectFactory;//扩展实例的属性获取Factory
下面是行为方法:
Public方法
getExtensionLoader
获取ExtensionLoader的唯一方式
然后会在方法内部调用构造器,构造器中为每一个ExtensionLoader生成一个ExtensionFactory实例
getAdaptiveExtension
大部分使用ExtensionLoader都会调用AdaptiveClass来进行选择处理
这个方法在第一次调用的时候会载入SERVICES_DIRECTORYDUBBO_DIRECTORY文件里面对应的ClassName,所以这里是延迟载入
其余的Public方法没什么好说的
private方法
在getAdaptiveExtension中载入的时候调用过程如下
getAdaptiveExtension--createAdaptiveExtension--getAdaptiveExtensionClass--getExtensionClasses(载入文件ClassName)-----如果没有AdaptiveClass-----就会通过createAdaptiveExtensionClass字节码生成AdaptiveClass-------injectExtension
getAdaptiveExtension
public T getAdaptiveExtension() { Object instance = cachedAdaptiveInstance.get(); if (instance == null) { if(createAdaptiveInstanceError == null) { synchronized (cachedAdaptiveInstance) { instance = cachedAdaptiveInstance.get(); if (instance == null) { try { instance = createAdaptiveExtension(); cachedAdaptiveInstance.set(instance); } catch (Throwable t) { createAdaptiveInstanceError = t; rethrowAsRuntime(t, "fail to create adaptive instance: "); } } } } else { rethrowAsRuntime(createAdaptiveInstanceError, "fail to create adaptive instance: "); } } return (T) instance; }
createAdaptiveExtension--创建AdaptiveExtension
private T createAdaptiveExtension() { try { return injectExtension((T) getAdaptiveExtensionClass().newInstance()); } catch (Exception e) { throw new IllegalStateException("Can not create adaptive extenstion " + type + ", cause: " + e.getMessage(), e); } }
getAdaptiveExtensionClass--获取AdaptiveExtension里面包含了2中AdaptiveExtension来源
private Class<?> getAdaptiveExtensionClass() { getExtensionClasses(); if (cachedAdaptiveClass != null) { return cachedAdaptiveClass; } return cachedAdaptiveClass = createAdaptiveExtensionClass(); }
getExtensionClasses方法装配文件,
然后判断有没有cachedAdaptiveClass
如果没有createAdaptiveExtensionClass字节码创建
injectExtension方法--通过objectFactory来对AdaptiveExtensionInstance进行DI。
下面来说说这个
createAdaptiveExtensionClass中的
createAdaptiveExtensionClassCode方法
通过字节码生成AdaptiveClass
但是
字节码生成的AdaptiveClass严重依赖URL(主要是依赖URL里面的protocol)。。看起来不那么优雅。
ExtensionLoader作为系统核心Loader模式,不应该过分只为Protocol服务。